Cold storage apparatus

ABSTRACT

Cold storage apparatus comprises a vessel (1) containing a storage liquid and a heat transfer liquid in direct contact with the storage liquid to transfer heat thereto or therefrom. The liquids are immiscible and of different densities and the heat transfer liquid remains liquid during heat transfer. The storage liquid comprises a liquid which solidifies when sufficiently cooled by the heat transfer liquid and the solidified storage liquid is of a different density to the storage liquid. The liquids form by gravity sequentially within the vessel (1) a first layer (4) of heat transfer liquid, a second layer (3) of storage liquid and a third layer (2) of solidified storage liquid. The cold storage apparatus includes heat transfer liquid circulating means (6) to deliver the heat transfer liquid to and from vessel (1). The heat transfer liquid circulating means (6) is arranged to deliver the heat transfer liquid into the first or second layer (4) or (3) at a temperature below the freezing point of the storage liquid.

The present invention relates to cold storage apparatus and inparticular to ice storage apparatus.

Ice storage provides the means to shift electrical load for cooling forinstance air conditioning systems. As shown in FIG. 1, during off peakperiods the chiller plant runs to charge up the ice store and thenduring peak periods (day time periods) the store can be used to providesome or all of the buildings' cooling requirements.

Much work has been done in developing an efficient means of providingcold storage in the form of ice store. An efficient cold storage methodfor producing ice uses a direct contact evaporator. Such an arrangementis disclosed in U.S. Pat. No. 4,864,831. In this arrangement arefrigerant is brought into direct contact with water in a tank to formice which is used for heat exchange to provide chilled water for use inair conditioning. The refrigerant is sprayed onto or into the water andevaporates to absorb its latent heat of evaporation from the water, thusforming ice. The evaporating gaseous refrigerant is then condensed andrecirculated. Although this method has an advantage of direct contactbetween the refrigerant (heat transfer fluid) and the water (storageliquid), it is important to ensure that no water vapour is carried overwith the refrigerant vapour to the compressor if conventionalcompressors are to be used. Otherwise, non-conventional compressors mustbe used.

Thus the object of the present invention is to provide a direct contactcold storage apparatus which avoids the problem of water vapour beingcarried over with the refrigerant vapour and provides for efficient heattransfer.

The present invention provides cold storage apparatus comprising avessel containing a storage liquid and a heat transfer liquid in directcontact with said storage liquid to transfer heat thereto or therefrom,said liquids being immiscible and of different densities, said heattransfer liquid remaining liquid during heat transfer, said storageliquid comprising a liquid which solidifies when sufficiently cooled bysaid heat transfer livid, the solidified storage liquid having adifferent density to said storage liquid, said liquids forming bygravity sequentially within said vessel a first layer of said heattransfer liquid, a second layer of said storage liquid, and a thirdlayer of said solidified storage liquid; said cold storage apparatusincluding heat transfer liquid circulating means to deliver said heattransfer liquid to and from said vessel, said heat transfer liquidcirculating means being arranged to deliver said heat transfer liquidinto said first layer or said second layer at a temperature below thefreezing point of said storage liquid.

Preferably the heat transfer liquid circulating means is arranged todeliver the heat transfer liquid into said second layer.

Preferably said solidified storage liquid is less dense that saidstorage liquid, and said heat transfer liquid is denser than saidstorage liquid. Conveniently in such an arrangement said storage liquidcomprises water.

In one embodiment said heat transfer liquid circulating means isarranged to inject said heat transfer liquid in the form of dropletsinto said second layer.

In one embodiment feed means are provided to inject the storage liquidfrom the second layer into the heat transfer liquid in the heat transferliquid circulating means at a position before the heat transfer liquidenters said second layer.

In one embodiment said feed means includes a pump to pump said storageliquid into said heat transfer liquid.

In another embodiment said heat transfer liquid circulating meansincludes a circulating conduit, and said feed means comprises a venturiarranged in said conduit, said venturi having an opening in a wall of aconstricted part thereof, through which in use said storage liquidpasses into said heat transfer liquid.

Preferably the heat transfer liquid circulating means includes a pumpand heat exchange means.

In one embodiment a refrigeration circuit is coupled to the heatexchanging means to cool the heat transfer liquid.

To allow for the discharge of the coolth from the cold storageapparatus, in one embodiment the apparatus includes storage liquidcirculating means for discharging coolth to a load to be cooled.

In one embodiment the storage liquid circulating means is arranged tocirculate said storage liquid from said second layer into said thirdlayer.

In another embodiment the storage liquid circulating means is arrangedto circulate said solidified storage liquid from said third layer intosaid second layer.

Preferably said storage liquid circulating means includes a pump andheat exchange means.

The present invention thus provides a direct contact cold storageapparatus wherein the heat transfer liquid remains liquid during theheat transfer process. The preferred use of a heat transfer liquid whichis denser than the storage liquid and the use of a storage liquid suchas water wherein the frozen material is less dense than the liquidmaterial, avoids the build-up of an ice boundary between the heatexchange liquid and the storage liquid. This provides for efficient heattransfer.

Examples of the present invention will now be described with referenceto the drawings in which:

FIG. 1 is an illustration of the electrical load for a cold storageapparatus according to one embodiment of the present invention;

FIG. 2 illustrates a cold storage apparatus according to a firstembodiment of the present invention;

FIG. 3 illustrates the use of a venturi for the feed means in thearrangement of FIG. 2;

FIG. 4 illustrates a cold storage apparatus according to a secondembodiment of the present invention;

FIG. 5 illustrates a cold storage apparatus according to a thirdembodiment of the present invention.

FIG. 6 illustrates an arrangement for discharging the cold storageapparatus.

FIG. 7 illustrates a further arrangement for discharging the coldstorage apparatus.

Referring now to FIG. 2, the vessel 1 contains a storage liquid which isconveniently water. In the vessel 1 when the water is cooled by the heattransfer liquid it solidifies to form an ice slurry layer 2 which floatson a water layer 3. The ice formed in the vessel has a lower densitythan water and will thus float to the top of the vessel 1.

At the bottom of the vessel 1, there is a layer of heat transfer liquid4. This liquid is of a higher density and is immiscible with water. Thusa clear boundary is formed between the heat transfer liquid 4 and thewater 3. Circulation means 6 is provided to circulate the heat transferliquid 4 from the bottom of the vessel via a heat exchanger 5 into thewater layer 3 in the vessel 1. The circulating means 6 comprises anoutlet pipe 8 connected to the bottom of the vessel 1 and a pump 7, asecond pipe 9 connecting the pump 7 to the heat exchanger 5 and a thirdpipe 10 connecting the heat exchanger 5 to an intermediate position inthe vessel 1 adjacent the water layer 3.

The heat transfer liquid 4 being circulated through the circulatingmeans 6 is cooled by the heat exchanger 5 which is coupled to arefrigeration circuit 11. The refrigeration circuit 11 comprises a pump17, a condensor 13 and an expansion device 12.

Thus the circulating means 6 circulates heat transfer liquid 4 from thebottom of the vessel 1 and intersperses the heat transfer liquid 4 inthe water 3. Thus heat exchange between the water 3 and the heatexchange liquid 4 takes place and ice formed in the water 3 rises tojoin the layer of ice 2 and the heat transfer liquid 4 falls to thebottom of the vessel 1. This provides for good heat exchange since thereis no ice build-up at the interface between the water and the heattransfer liquid.

To improve the heat exchange between the heat exchange fluid 4 and thewater 3, feed means 14 which in the illustrated arrangement includes apump 15 injects water 3 from the vessel 1 into the pipe 10. Thisarrangement facilitates the formation of droplets of water within theheat transfer liquid which droplets are well dispensed throughout theheat transfer liquid. Such provides for excellent heat transfer betweenthe water and the heat transfer liquid in view of the increasedinterfacial surface area. Thus even before the heat transfer liquid hasreached the vessel 1, some heat transfer to form ice will have alreadytaken place.

FIG. 3 illustrates a modification to the feed means 14 in FIG. 2. Inthis arrangement no pump 15 is required. Instead a venturi 50 isprovided in the third pipe 10. The venturi 50 provides a pressure dropthereacross. An opening 51 is provided in the wall of the venturi at aposition where the cross sectional area of the orifice 52 is at itssmallest. The opening 51 communicates with the feed means 14 such thatwater from the water layer 3 is injected into the heat transfer liquidflowing in the third pipe as a result of the pressure drop. Turbulencewithin-both the venturi 50 and the third pipe 10 will enhance theformation of droplets of water within the heat transfer liquid and willincrease the homogeneity of the distribution of the droplets, thusimproving heat transfer between the liquids.

FIG. 4 illustrates a further embodiment of the present invention whereinonce again like reference numerials refer to like features. In thisembodiment the heat transfer liquid 4 is removed from the bottom of thevessel 1 and is injected into the heat transfer layer 4 via the pipe 10whereupon it fountains into the water layer 3 in order to interspersethe heat transfer liquid 4 in the water 3 and provide efficient heattransfer.

FIG. 5 illustrates a further embodiment of the present invention whereinthe arrangement is similar to that of the embodiment illustrated in FIG.4 except that the ice 2 formed at the top of the vessel 1 is deliveredto a storage vessel 20, by circulating means 21. A pump 22 is providedto deliver water 3 from the storage vessel 20 into the vessel 1, whereupon the water 3 is cooled and frozen by the interspersion of the heattransfer liquid 4 being injected into the vessel 1. This arrangementprovides for a separate storage vessel 20 for the ice being produced inthe vessel 1.

In both of the arrangements illustrated in FIGS. 4 and 5 the feed means14 of FIGS. 2 and 3 can be incorporated to improve heat exchange.

These embodiments of the present invention illustrate the advantage ofusing a heat transfer fluid which is denser than the storage fluid, anda storage fluid which when frozen has a lower density than the liquid.the chiller performance is unaffected by the amount of ice that has beenproduced, and the ice produced is in the form of a slurry to give gooddischarge characteristics.

Liquids that have been identified as being suitable as the heat transferliquid in the embodiments described hereinbefore are 1.1.1trichloroethane, 1.1.2 trichloroethylene and perflourohexane. Suchliquids are immiscible with water and remain liquid over the temperaturerange of operation.

To enchance the separation of water and the heat transfer liquid, inaddition to gravity other separation techniques can be used such aselectrostatic filters, hydrocyclones, static filters and centrifugation.

To discharge the cold storage apparatus, either water or heat transferfluid can be passed through the ice store to a heat exchanger in thermalcontact with the load to be cooled, or the ice slurry can be circulateddirectly to the load.

FIG. 6 illustrates an arrangement for discharging the cold storageapparatus in combination with the arrangement for charging the coldstorage apparatus. The arrangement for charging is the same as thatshown in FIG. 2 and like reference numerals have been used to denotelike components.

In the arrangement of FIG. 6 the refrigeration circuit differs in that atwo way valve 30 is provided between the pump 17 and the heat exchanger5. At the other side of the heat exchanger 5 is provided a first cut offvalve 31. Thus during charging the two way valve 30 is set to pass heatexchange fluid within the refrigeration circuit 11 through the heatexchanger 5 to cool the heat exchange liquid 4.

During discharge the two way valve 30 is set to pass heat exchange fluidwithin the refrigeration circuit 11 through a second heat exchanger 35which is provided with a second cut of valve 32 at the other side. Thesecond heat exchanger 35 is provided within a discharge refrigerationloop generally indicated by reference numeral 33.

In the discharge refrigeration loop water 3 is pumped from the vessel 1using a pipe 34 by a pump 36 via a two way valve 37 to a load 38 to coolthe load 38. The water leaving the load 38 which has been heated by theload is passed to the second heat exchanger 35 so that the refrigerationcircuit can provide some cooling, and then it is passed by the pipe 34into the vessel 1 wherein it is sprayed onto the ice slurry 2 by nozzle39.

In this arrangement cooling of the load is provided by both therefrigeration circuit 11 and the ice store in the vessel 1.

Referring now to FIG. 7, in this drawing an arrangement is shown for thedischarge of the cold storage apparatus. In this arrangement ice slurry2 is pumped from the vessel 1 by the slurry pump 40 and passed directlythrough the load 41 before being returned to the vessel 1 at the levelof the water 3.

Thus as illustrated in FIGS. 6 and 7 the stored cool can be dischargedand used to cool a load either in combination with a refrigerationcircuit or on its own.

I claim:
 1. Cold storage apparatus comprising a vessel containing astorage liquid and a heat transfer liquid in direct contact with saidstorage liquid to transfer heat thereto or therefrom, said liquids beingimmiscible and of different densities, said heat transfer liquidremaining liquid during heat transfer, said storage liquid comprising aliquid which solidifies when sufficiently cooled by said heat transferliquid, the solidified storage liquid having a different density to saidstorage liquid, said liquids forming by gravity sequentially within saidvessel a first layer of said heat transfer liquid, a second layer ofsaid storage liquid, and a third layer of said solidified storageliquid; said cold storage apparatus including heat transfer liquidcirculating means to deliver said heat transfer liquid to and from saidvessel, said heat transfer liquid circulating means being arranged todeliver said heat transfer liquid directly into said second layer at atemperature below the freezing point of said storage liquid, andincluding feed means to inject said storage liquid from said secondlayer into said heat transfer liquid in said heat transfer liquidcirculating means at a position before said heat transfer liquid enterssaid second layer.
 2. Cold storage apparatus as claimed in claim 1 orwherein said solidified storage liquid is less dense than said storageliquid, and said heat transfer liquid is denser than said storageliquid.
 3. Cold storage apparatus as claimed in claim 2 wherein saidstorage liquid comprises water.
 4. Cold storage apparatus as claimed inclaim 1 including a storage vessel containing said storage liquid andsaid solidified storage liquid, and circulating means to deliver saidstorage liquid from said storage vessel to said vessel and return saidsolidified storage liquid from said vessel to said storage vessel. 5.Cold storage apparatus as claimed claim 1 wherein said heat transferliquid circulating means is arranged to inject said heat transfer liquidin the form of droplets into said second layer.
 6. Cold storageapparatus as claimed in claim 5 wherein said feed means includes a pumpto pump said storage liquid into said heat transfer liquid.
 7. Coldstorage apparatus as claimed in claim 1 wherein said heat transferliquid circulating means includes a circulating conduit and said feedmeans comprises a venturi arranged in said conduit, said venturi havingan opening in a wall of a constricted part thereof, through which in usesaid storage liquid passes into said heat transfer liquid.
 8. Coldstorage apparatus as claimed in claim 1 wherein said heat transferliquid circulating means includes a pump and heat exchanging means. 9.Cold storage apparatus as claimed in claim 8 further including arefrigeration circuit coupled to said heat exchanging means to cool saidheat transfer liquid.
 10. Cold storage apparatus as claimed in claim 1including storage liquid circulating means for discharging coolth fromsaid storage liquid to a load to be cooled.
 11. Cold storage apparatusas claimed in claim 10 wherein said storage liquid circulating means isarranged to circulate said storage liquid from said second layer intosaid third layer.
 12. Cold storage apparatus as claimed in claim 10wherein said storage liquid circulating means is arranged to circulatesaid solidified storage liquid from said third layer to said secondlayer.
 13. Cold storage apparatus as claimed in claim 10 wherein saidstorage liquid circulating means includes a pump and heat exchangingmeans.
 14. Cold storage apparatus comprising a vessel containing astorage liquid and a heat transfer liquid in direct contact with saidstorage liquid to transfer heat thereto or therefrom, said liquids beingimmiscible and of different densities, said heat transfer liquidremaining liquid during heat transfer, said storage liquid comprising aliquid which solidifies when sufficiently cooled by said heat transferliquid, the solidified storage liquid having a different density to saidstorage liquid, said liquids forming by gravity sequentially within saidvessel a first layer of said heat transfer liquid, a second layer ofsaid storage liquid, and a third layer of said solidified storageliquid; said cold storage apparatus including heat transfer liquidcirculating means to deliver said heat transfer liquid to and from saidvessel, said heat transfer liquid circulating means being arranged todeliver said heat transfer liquid into said second layer at atemperature below the freezing point of said storage liquid, andincluding a storage vessel containing said storage liquid and saidsolidified storage liquid, and circulating means to deliver said storageliquid from said storage vessel to said first mentioned vessel andreturn said solidified storage liquid from said first mentioned vesselto said storage vessel.
 15. Cold storage apparatus as claimed in claim14 wherein said solidified storage liquid is less dense than saidstorage liquid, and said heat transfer liquid is denser than saidstorage liquid.
 16. Cold storage apparatus as claimed in claim 15wherein said storage liquid comprises water.
 17. Cold storage apparatusas claimed in claim 14 wherein said heat transfer liquid circulatingmeans is arranged to inject said heat transfer liquid in the form ofdroplets into said second layer.
 18. Cold storage apparatus as claimedin claim 14 wherein said heat transfer liquid circulating means includesa pump and heat exchanging means.
 19. Cold storage apparatus as claimedin claim 18 further including a refrigeration circuit coupled to saidheat exchanging means to cool said heat transfer liquid.
 20. Coldstorage apparatus as claimed in claim 14 including storage liquidcirculating means for discharging coolth from said storage liquid to aload to be cooled.
 21. Cold storage apparatus as claimed in claim 20wherein said storage liquid circulating means is arranged to circulatesaid storage liquid from said second layer into said third layer. 22.Cold storage apparatus as claimed in claim 20 wherein said storageliquid circulating means is arranged to circulate said solidifiedstorage liquid from said third layer to said second layer.
 23. Coldstorage apparatus as claimed in claim 20 wherein said storage liquidcirculating means includes a pump and heat exchanging means.
 24. Coldstorage apparatus comprising a vessel containing a storage liquid and aheat transfer liquid in direct contact with said storage liquid totransfer heat thereto or therefrom, said liquids being immiscible and ofdifferent densities, said heat transfer liquid remaining liquid duringheat transfer, said storage liquid comprising a liquid which solidifieswhen sufficiently cooled by said heat transfer liquid, the solidifiedstorage liquid having a different density to said storage liquid, saidliquids forming by gravity sequentially within said vessel a first layerof said heat transfer liquid, a second layer of said storage liquid, anda third layer of said solidified storage liquid; said cold storageapparatus including heat transfer liquid circulating means to deliversaid heat transfer liquid to and from said vessel, said heat transferliquid circulating means being arranged to deliver said heat transferliquid into said second layer at a temperature below the freezing pointof said storage liquid, and including storage liquid circulating meansfor discharging coolth from said storage liquid to a load to be cooled.25. Cold storage apparatus as claimed in claim 24 wherein saidsolidified storage liquid is less dense than said storage liquid, andsaid heat transfer liquid is denser than said storage liquid.
 26. Coldstorage apparatus as claimed in claim 25 wherein said storage liquidcomprises water.
 27. Cold storage apparatus as claimed in claim 24wherein said heat transfer liquid circulating means is arranged toinject said heat transfer liquid in the form of droplets into saidsecond layer.
 28. Cold storage apparatus as claimed in claim 24 whereinsaid heat transfer liquid circulating means includes a pump and heatexchanging means.
 29. Cold storage apparatus as claimed in claim 28further including a refrigeration circuit coupled to said heatexchanging means to cool said heat transfer liquid.